Is the target=_"top" attribute really necessary when creating a link to another website? If yes,why?

Answer 1

You should use target="_blank". The link will open in a new window/tab.
The other target names like _top were used with frames.

Answer 2

you can use
<a href="" target="_blank"></a>
to open link in new window and you can use
<a href="' target "_self"></a>
to open link in the same window